[SeaBIOS] Ideas for PV on SeaBIOS
kevin at koconnor.net
Sat May 21 15:29:49 CEST 2011
On Thu, May 19, 2011 at 02:33:52PM +0900, Daniel Castro wrote:
> Good Day,
> In order to give PV Drivers to SeaBIOS we will need to solve a few
> problems, one is the following:
> Does a booting kernel informs the BIOS that it will leave real mode
> and not use it again? When the booting kernel uses CPU real mode for
> the last time, how can we (Xen or SeaBIOS) know that real mode will no
> longer be used, and hence BIOS calls will not be issued?
In the general case, no.
The ACPI spec does define a mechanism for the OS to inform the BIOS
that it is transitioning from "Legacy state" to "Working state" via an
SMI. SeaBIOS does have code for this (see src/smm.c), but it doesn't
currently do anything interesting. Unfortunately, this is only
available for OSs that support ACPI.
> We want upon last real mode usage to leave all Xen PV information in a
> clean state, this means, closing the channel and ring between the
> newly created domain and the host system.
Is it required to close the channel? Can opening a new channel
implicitly close the old channel (I believe this is what the virtio
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